In vitro rehardening and staining effects of silver diamine fluoride with and without mucin on early enamel caries lesions

Purpose: To evaluate the rehardening ability of SDF and its individual components, silver, and fluoride ions, on early enamel caries lesions using artificial saliva with and without mucin. Methods: Early caries lesions were created in human permanent enamel specimens. The specimens (n=36 per group) were then treated with a single application of: SDF (38%), SDF followed by application of potassium iodide (SDF+KI), potassium fluoride (KF); fluoride control, 44,800 ppm (F), silver nitrate (AgNO3); silver control, 253,900 ppm (Ag), or deionized water (DIW). Immediately, the specimens were subjected to 4 days of continuous remineralization with or without mucin (n=18 per subgroup). Changes in Vickers surface microhardness from lesion baseline (Delta VHN) were calculated. Data were analyzed using two-way (intervention vs. rehardening models) ANOVA. Results: In both rehardening models (with or without mucin), SDF (Delta VHN data; mean +/- standard deviation; with/without mucin: 26 +/- 19/3 +/- 11) was significantly less effective in rehardening promotion than SDF+KI (37 +/- 12/39 +/- 16) and KF (40 +/- 17/41 +/- 29; P <= 0.0332). Compared to AgNO3 (9 +/- 9/18 +/- 15) and DIW (3 +/- 7/12 +/- 9), SDF was more effective in the presence of mucin (P <= 0.001) but not in its absence, similar to DIW (P= 0.1117); less effective vs. AgNO3 (P= 0.0061). The presence of mucin significantly increased the rehardening ability of SDF (P< 0.0001). However, mucin did not affect the extent of rehardening in the other groups (P >= 0.082). SDF+KI and KF were superior in their ability in rehardening promotion than AgNO3 and DIW in both rehardening models (P< 0.0001). In both rehardening models, Delta L* values from baseline to post-rehardening show that applying KI after SDF significantly lessened the dark staining caused by SDF (P< 0.0001). Under the present in vitro conditions, SDF does not appear to enhance surface rehardening of early enamel caries lesions. The co-presence of mucin during rehardening enhanced the efficacy of SDF which warrants further investigation.